Research On Vehicle Stability Experiments And Safety Of Surface Pathway During Road Flooding

Frequent urban flooding caused by global climate change and accelerating urbanization poses a great threat to the safety of vehicles under road flooding conditions.The surface flood pathway is a critical component of the urban drainage system and plays a key role in preventing and controlling urban flooding.However,the risk threshold for vehicles under road flooding conditions and the safety design of surface flood pathways for excess rainwater have not been given adequate attention.Through theoretical analysis and experimental research,experiments were conducted using three types of model vehicles with a ratio of 1:18.The objective was to investigate the relationship between the critical instability state of the vehicles and water depth and flow velocity,with the aim of clarifying the risk threshold for vehicle instability under road flooding conditions.Based on hydrodynamic theory,an evaluation index for flood risk in surface flood pathways is established,and a road flood risk rating map is created with the aim of ensuring traffic safety.By combining hydrological and hydraulic calculations,as well as model simulations,a method for assessing the flood risk level of surface flood pathways is proposed.The research results will provide theoretical guidance and scientific support for constructing road drainage systems and mitigating urban flooding.The main findings are as follows:(1)The buoyancy of the Polo GTI(small passenger car),Audi A6L(large passenger car),and Range Rover(large 4WD)exhibits a gradual increase with increasing water depth,but the rate of increase gradually decreases.The heavier the vehicle,the higher the threshold for floatation instability.Conversely,the larger the vehicle’s volume,the greater the buoyancy force it experiences,resulting in a lower threshold for floatation instability.As the vehicle size increases,the impact of increasing load on the instability threshold diminishes.The Polo GTI exhibits a floatation instability threshold of 359.3mm,the Audi A6L has a threshold of 378.8mm,and the Range Rover has a threshold of 459.0mm when unloaded.(2)The drag force and transverse force acting on a vehicle increase with the flow velocity and water depth.When the incoming flow direction changes from 0° to 90°,the drag force gradually increases,but when the direction changes from 90° to 180°,the drag force gradually decreases,showing a single-peak trend.On the other hand,the transverse force gradually increases as the flow direction moves from 0° to 45° and 90° to 135°,and decreases as the direction moves from 45° to 90° and 135° to 180°,showing a double-peaked trend.The vehicle experiences the greatest drag force when perpendicular to the incoming flow,while the least drag force is exerted when the front of the vehicle faces the incoming flow.Furthermore,when the incoming flow direction is 45° and 135°,the vehicle is subjected to the greatest transverse force due to the most pronounced asymmetric effect of the vehicle.(3)The drag coefficient(CD)and the transverse force coefficient(CT)were determined based on a linear fit of multiple sets of experimental results in the same direction of incoming flow.The drag coefficient values for the three vehicles in different incoming flow directions(0°to 180°)range between 1.22 and 6.82,while the values of the transverse force coefficient range from 0 to 2.40.(4)By combining theoretical force analysis and experimental research results,the risk threshold of vehicle instability was calculated,and the vehicle stability surfaces for different operating conditions were plotted.The stability of a vehicle under road flooding conditions depends on the water depth,flow velocity,and incoming flow direction.The vehicle’s stability is affected by the drag force,transverse force,and buoyancy force,which work synergistically.When the water depth is small,the drag force and transverse force have a greater influence on the vehicle’s stability,but as the water depth increases,the buoyancy force gradually becomes the dominant factor.The change in the vehicle’s stability with the incoming flow direction becomes less noticeable as the water depth increases.The higher the water depth,the lower the flow velocity threshold required for vehicle instability.When the incoming flow direction increases from 0° to 90°,the vehicle’s ability to resist instability gradually decreases,and the decrease tends to slow down at 45° to 90°.When the direction of incoming flow is 90° to 180°,the pattern is similar to that of the incoming flow direction from 0° to 90°,but the vehicle is less resistant to instability at this point than when the direction of incoming flow is 90° to 180°.(5)The flood risk evaluation index for surface flood pathways is determined by combining the water flow energy equation and the momentum equation,resulting in the product of the square of the water depth and the total energy per unit weight of the water flow,D2H.Based on the study on vehicle stability under road flooding conditions,the flood risk level of surface pathways is then classified.When D2H is less than or equal to 0.015,the risk level is considered safe.When D2H is between 0.015 and 0.050,the risk is low.If D2H falls between 0.050 and 0.150,the risk is considered medium.However,if D2H is greater than 0.150,the risk is high.The flood risk level of surface pathways is drawn accordingly based on these classifications.(6)Hydraulic calculation equations for different road cross-sections were derived using two expressions for water depth and spread,and a functional relationship between rainfall,catchment area,and road flood risk was established.Additionally,a road flood risk level assessment method based on the rational method is proposed.Results from global sensitivity analysis indicate that catchment area(F)and road cross-slope(Sx)have a significant impact on water depth and flood magnitude,with the influence of each parameter varying for different catchment area ranges.The simulation results were utilized to draw a simulation hydrograph for runoff and flood risk through the model simulation.And a model simulation-based method for assessing road flood risk levels is proposed.